1. Field of the Invention
The present invention relates to an optical scanning apparatus such as laser printer, laser plate-making machine, or the like which scans a light spot on a surface to be scanned.
2. Description of the Prior Art
Optical scanning apparatus such as laser printer, laser plate-making machine, and the like have conventionally been known, in which a light beam such as laser beam is scanned on a surface to be scanned made of a photosensitive material or the like so as to form an image on this surface. A light-scanning optical system employed in such an optical scanning apparatus comprises a light deflector such as rotary polygon mirror which reflects and deflects a light beam emitted from a light source such that the light beam is scanned on the surface to be scanned, and an imaging optical system for focusing the light beam onto the surface to be scanned.
In general, such an optical scanning apparatus is provided with an imaging optical system, comprising various kinds of lenses, disposed in front of or behind the light deflector, while an f .theta. lens is located in the last stage thereof.
When various kinds of lenses are thus interposed between the light source and the surface to be scanned, however, then the overall length of the optical path inevitably increases, thereby making it difficult for the apparatus to have a compact size.
Also, in such an imaging optical system, the heat from the light source and the rotation of the light deflector may generate turbulence in the air, thereby adversely affecting the optical scanning. Hence, there has been a demand for a technique which can suppress the influence of the air turbulence as much as possible even under such an environment.
Further, there has been a strong demand for a technique which reduces the number of components of optical members constituting the imaging optical system while favorably maintaining its imaging performances, thereby making the apparatus compact and cutting down its manufacturing cost.
In view of such circumstances, it is an object of the present invention to provide an optical scanning apparatus which can shorten the overall length of the optical path in the air between the light source and the surface to be scanned, thereby being able to make the apparatus compact and reduce its manufacturing cost while alleviating the adverse effects caused by the turbulence in the air.
In optical scanning apparatus, on the other hand, there has generally been known a configuration in which, in order to control the timing of optical scanning on the surface to be scanned, a luminous flux scanned outside the surface by the light deflector is received by a light-receiving sensor, and the timing of the optical scanning is controlled according to the resulting light-receiving timing.
Such a luminous flux for controlling the optical scanning timing has also been required to shorten the overall length of its optical path in the air so as to make the apparatus compact. Further, it is desirable to alleviate the adverse effects caused by the turbulence in the air due to the heat from the light source and the rotation of the light deflector with respect to such a luminous flux as well.
It is thus another object of the present invention to allow a luminous flux for controlling the timing of optical scanning in the optical scanning apparatus to have a shorter overall length of the optical path in the air, thereby making the apparatus compact and alleviating the adverse effects caused by the turbulence in the air on the luminous flux.